Many processes and various types of equipment have been proposed and used heretofore for making compost from animal waste. To my knowledge such equipment and processes have had one or more drawbacks or disadvantages. Some of the equipment heretofore used or proposed is extremely costly and impractical. Likewise, the prior art processes for the most part involve a relatively long period of time to complete the composting action and produce a compost having a relatively low nutrient value, especially with reference to its nitrogen content.
Organic waste is converted into compost by the process of fermentation. The waste is usually mixed with organic carbonaceous filler material and, when the mixture is agitated and aerated, the process of fermentation progresses through several states to decompose the mixture and produce the compost.
The first stage of the fermentation process is characterized by the production of and multiplication of aerobic bacteria in the presence of moisture and air. This reaction generates heat and the decomposition is then continued by thermophilic aerobic bacteria. With proper control of the moisture content and aeration, heat is generated as the mixture decomposes and the temperature of the mixture progressively rises to an optimum value. The mixture remains at this elevated temperature while the decomposition process continues for a period of time, depending upon such variable conditions as moisture content, manner and extent of aeration, and the nature of the mixture ingredients. Thereafter the mixture gradually cools. When the mixture reaches a predetermined low temperature (usually considered to be about 100.degree. F.) the production of aerobic bacteria ceases and the reaction then becomes anaerobic where anaerobic bacteria and fungi take over and further decompose the the mixture, particularly the cellulose therein, in the presence of moisture, but without further aeration required.
I have determined that the maximum nutrient value of the compost is obtained at the completion of the aerobic thermophilic reaction, provided the reaction proceeds under optimum operating conditions. If, after the aerobic reaction is completed, the mixture is permitted to undergo an anaerobic reaction for a prolonged period of time, the nutrient value of the compost (the nitrogen content in particular) actually decreases. In accordance with the present invention the moisture content of the compost is reduced to a predetermined maximum value by drying the compost within a reasonably short period of time after the aerobic reaction is completed. As a practical matter and for reasons of economy the compost is permitted to cool to room temperature or about 100.degree. F. in the composting chamber. The compost is then transferred to a dryer where its moisture content is reduced to less than 50% by weight and is thereafter promptly packaged in containers which are generally moisture impervious so that the anaerobic reaction is arrested and prevented from re-occurring. In this manner I have been able to produce compost having a nitrogen content as high as 18% and consistently higher than 7% from a mixture containing approximately 4% chicken manure and 60% sawdust in a period of 30 to 40 hours.
I believe that the high nutrient value of the compost and the relatively short period of time involved in producing the compost according to the present invention is also attributable to the manner and the extent to which the mixture is aerated. The aerobic thermophilic reaction is maximized when all portions of the mass are slowly aerated uniformly and to the proper extent. In order to aerate the mixture properly it is necessary to agitate the whole mass very slowly in such a manner that substantially all portions thereof are exposed to an optimum amount of air for an optimum period of time. If the mass is agitated too violently or if the amount of air is excessive, the mixture will be dried and cooled. On the other hand, if the air supplied is less than the optimum amount required or if the mass is not agitated properly the bacterial activity will not reach its maximum potential and the composting process will require an unduly long period of time. In other words, if the temperature of the mixture does not reach the maximum or optimum value to allow the reaction to progress at its maximum potential rate the process becomes a costly one and the compost will not normally have a relatively high fertilizer value.
It has been recognized in the past that agitation and aeration of the mixture is conducive to the rate at which the organic waste will be converted to compost. In the past agitation of the mixture has been accomplished by such means as horizontally reciprocating or linearly moving rakes or plows and rotary drums with or without baffles or radial fingers projecting into the mixture. With such types of equipment the proper aeration has not been achieved. For example, with rakes it is impractical, if not impossible, to agitate the mass so that the oxygen in the air will come into intimate contact with all portions thereof for the required time interval. In the case of rotary drums, some portions of the mass remain stagnant for an unduly long period of time while other portions are caused to fall or tumble rapidly through the air stream directed through the drum. In either case, substantially all portions of the mixture in the drum are not uniformly exposed to the air for the required period of time to achieve the optimum operating conditions to allow the reaction to progress at its maximum potential rate and to produce the maximum nutrient content.